As hydrocarbon fields are growing more mature, the established methods of producing oil are no longer sufficient to exploit a reservoir to the extent theoretically possible. In response to this challenge a plethora of new methods have been proposed to increase recovery beyond that afforded by established methods. These methods are generally referred to as “Enhanced Oil Recovery” or EOR treatments.
Many EOR treatments make use of the injection of heat in form of heated fluids, the injection of gas (Methane, Nitrogen, Carbon Dioxide, etc.) together or alternating with water injection, or the injection of chemicals such as surfactants. Whilst a great number of such methods have been described in the relevant literature and even used in the field, it is to be expected that more and improved EOR treatments will be developed in the future.
The emergence of a multitude of EOR treatments have in common the need for thorough testing prior to large scale implementation in a reservoir. In spite of this need, testing methods have been limited in the past to laboratory test and field pilot tests.
Typically for a laboratory test, an enclosed rock core is subjected to the EOR method to be tested. Obviously, it is a very challenging task for the experimenter to emulate all downhole conditions in the laboratory and, hence, the results of such core flooding tests are often found to be only a loose indicator of the efficacy of an EOR method.
For testing under real downhole conditions, operators rely on the use of pilot tests. Typically such pilot tests are limited field deployments with for example one testing injector well and a small number of producing wells in the vicinity of the injector well, such as in a “five-spot” pattern. Given even the minimal distance between two separate wells and typical permeability values of the rock formation between these wells, it takes in most cases years before the effectiveness of an EOR treatment becomes measurable. In addition, such pilot tests require significant up-front investment in materials and equipment prior to having complete knowledge of the efficacy of the EOR treatment in question.
An early example of these methods is described in U.S. Pat. No. 3,393,735 issued to Altamira and Hoyt, whereas other examples of EOR testing include co-owned U.S. Pat. No. 4,085,798 to Schweitzer and Tapphorn, U.S. Pat. No. 5,467,823 to Babour et al. and the more recent co-owned U.S. Pat. No. 6,886,632 to Raghuraman and Auzerais, U.S. Pat. No. 6,588,266 to Tubel et al., as well as the patents and literature sources referenced in these patents.
In an effort to shorten the time required to test an EOR treatment, it has been proposed to use laterals or fractures within a well. Early examples of these single well methods are described in U.S. Pat. No. 3,159,214 to Carter and U.S. Pat. No. 3,163,211 to Henley. Further methods to place sensors in micro-boreholes drilled from the main well are described for example in co-owned U.S. Pat. No. 6,896,074 to Cook et al.
In the light of the above cited prior art, it is seen as an object of the present invention to provide improved testing methods for EOR treatments, particularly single-well and dual-well testing methods.